Arctic Circle
The Arctic Circle is one of the two polar circles, and the northernmost of the five major circles of latitude. It is shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle.
The Arctic Circle marks the southernmost latitude for which at the December solstice the Sun does not rise and at the June solstice the Sun does not set. These phenomena are referred to as polar night and midnight sun, respectively, and the closer to the pole one goes, the longer that situation persists. For example, in the Russian port city of Murmansk the Sun stays below the horizon for 20 days before and after the winter solstice, and above the horizon for 20 days before and after the summer solstice.
The positions of the Arctic and Antarctic Circles vary slightly from year to year. Currently the Arctic Circle is north of the Equator. Its latitude depends on Earth's axial tilt, which fluctuates by a margin of some 2° over a 41,000-year period due to tidal forces resulting from the orbit of the Moon. Consequently, in the current epoch the Arctic Circle is drifting toward the North Pole, while the Antarctic Circle drifts towards the South Pole, each at a speed of about per year.
Etymology
The word arctic comes from the Greek word ἀρκτικός and that from the word ἄρκτος.Midnight sun and polar night
The Arctic Circle is the southernmost latitude in the Northern Hemisphere at which the centre of the Sun can remain continuously above or below the horizon for twenty-four hours; as a result, at least once each year at any location within the Arctic Circle the centre of the Sun is visible at local midnight, and at least once the centre is not visible at local noon.Directly on the Arctic Circle these events occur, in principle, exactly once per year: at the June and December solstices, respectively. However, because of atmospheric refraction and mirages, and also because the sun appears as a disk and not a point, part of the midnight sun is visible, on the night of the northern summer solstice, at a latitude of about 50 minutes of arc south of the Arctic Circle. Similarly, on the day of the northern winter solstice, part of the Sun may be seen up to about 50′ north of the Arctic Circle. That is true at sea level; those limits increase with elevation above sea level, although in mountainous regions there is often no direct view of the true horizon.
Human habitation
The largest communities north of the Arctic Circle are situated in Russia, Norway, and Sweden: Murmansk and Norilsk in Russia; Tromsø in Norway, Vorkuta in Russia, Bodø and Harstad in Norway; and Kiruna, Sweden. In Finland, the largest settlement in the immediate vicinity of the Arctic Circle is Rovaniemi, lying south of the line. Salekhard in Russia is the only city in the world located directly on the Arctic Circle.In contrast, the largest North American community north of the Arctic Circle, Sisimiut, has approximately 5,600 inhabitants. In the United States, Utqiagvik, Alaska is the largest settlement north of the Arctic Circle with about 5,000 inhabitants. The largest such community in Canada is Inuvik in the Northwest Territories, with 3,137 inhabitants.
Geography
The Arctic Circle is roughly in circumference. The area north of the Circle is about and covers roughly 4% of Earth's surface.The Arctic Circle passes through the Arctic Ocean, the Scandinavian Peninsula, North Asia, Northern America, and Greenland. The land within the Arctic Circle is divided among eight countries: Norway, Sweden, Finland, Russia, the United States, Canada, Denmark, and Iceland.